1. Field of the Invention
This invention relates to a fuel injection valve used for the internal-combustion engine, and in particular, to a fuel injection valve which has a movable part operated electro-magnetically to open and close a fuel passage.
2. Description of the Related Art
The conventional fuel injection valve of this kind, as described in Japanese Unexamined Patent Application No. 58-178863 or in Japanese Unexamined Patent Application No. 2006-22721, has its movable part configured to include an anchor section in a cylinder like shape, a plunger section located in the center part of the anchor section, and a valve plug provided on the leading end of the plunger section; further, magnetic gap is provided between the end face of a fixed core which has a fuel introduction hole to introduce fuel to the central part and the end face of the anchor, and a magnetic coil is also provided to supply magnetic flux to the magnetic passage including this magnetic gap.
By the magnetic flux penetrating through the magnetic gap, power of magnetic attraction is generated between the end face of the anchor and the end face of the fixed core so as to attract the anchor to the side of the fixed core driving the movable part; thereby it is so configured that the valving element is pulled away from the valve seat permitting the fuel passage in the valve seat to be opened.
In the case of a fuel injection valve configured as above, the collision faces between the end face of the anchor and the end face of the fixed core may stick to each other causing a problem that after the magnetic force has disappeared from the magnetic passage way, it takes a longer time than otherwise for the two sticky faces to return to the default position (a state where the faces get drawn fully apart thus pushing the valving element against the valve sheet).
One of the conceivable reasons for the above is because the anchor and the fixed core get magnetized in the surface to become held to each other by attraction of magnet. One's ingenuity, therefore, should be used here to prevent magnetization of these parts as much as possible.
Another conceivable reason for the above sticky faces is because fluidic cohesion phenomenon occurs when the anchor is attracted and the valve closing motion starts from the opened state of the valve in which the end face of the anchor and the end face of the fixed core are in contact with each other, that is, when separation begins between the end faces of the anchor and the fixed core gradually enlarging the gap for magnetic attraction.
Specifically, the strength of the fluidic force arising in the movement of pasting the anchor on to the fixed core has a property of being proportional to the moving speed of the anchor and inversely proportional to the cube of the gap width.
However, immediately after the open state of the valve starts to transfer to the starting state of closing the valve, the gap is yet too small to permit fluid freely flowing into the gap from the outside. Besides, inertia-gravity of the fluid surrounding the anchor obliges the anchor to move only at a very slow speed. The effect of the above phenomena denotes the behavior as if the end face of the anchor might seem to be pasted on the end face of the fixed core.
In order to moderate the above phenomena, it is important not to disturb, but resultantly to promote a smoother flow of fuel which occurs between the end face of the anchor and the end face of the fixed core and also around the anchor.
In an attempt to alleviate the above problem, a technology disclosed in the conventional art refers to a solution in which only a partial area is to be used as the collision face between the end face of the anchor and the end face of the fixed core so as to make the cohesion phenomenon difficult to occur, thereby preventing sticking.